In manufacturing a pneumatic tire, in order to relieve static electricity accumulated in a vehicle to the ground by ensuring electric conductivity of the tire, a tread having a base pen structure including a conductive layer is used, with ends of the tread covered by sidewalls (SOT structure).
Specifically, first, a sidewall is wrapped on opposite side portions of a first forming drum and, thereafter, on the central portion of the first forming drum, an inner liner and a ply are pasted successively. Then, a pair of beads is set inside the sidewalls, at positions corresponding to the width of the tire product. Thus, the first cover is formed (first cover forming step).
On the other hand, in parallel with the formation of first cover, on a second forming drum, a breaker and a band such as JLB (jointless band) are pasted and thereafter, a tread is wrapped by strip-winding, whereby a tread ring is formed (tread ring forming step).
The above-described tread having the base pen structure is formed in accordance with such process steps as shown in FIG. 7, at the tread ring forming step. First, as shown in FIG. 7(a), rubber strips of a composition having high solid specific resistance are stacked to form a tread layer 14. Thereafter, as shown in FIG. 7(b), rubber having low solid specific resistance is stacked thin along the tread layer 14 to form a conductive layer 15. Then, as shown in FIG. 7(c), a tread layer 14 is again formed on the outer side of conductive layer 15. In this manner, a tread having the base pen structure is formed, ensuring a path to relieve static electricity.
Then, the first cover is inserted to the inside of tread ring, and that portion of the first cover which is between the beads is inflated and pressure-bonded to the tread ring, to form a shape close to that of the low cover (shaping step).
Thereafter, in order that the tread is pressure-bonded to the first cover with no gap left therebetween, sides of tread are pressed by using a stitcher so that the sides extend along a curved side surface of the first cover that has been pressure-bonded to the tread ring (stitch-down step).
Thereafter, the sidewall outer than the bead is turned up toward the side surface of inflated first cover, and the sidewall is pasted to cover the tread end (turn-up step). In this manner, the first cover and the tread ring are integrated and the formation of low cover is completed (for example, see Patent Documents 1, 2).